At a production plant or the like, there is a case when the plant is unmanned or automated by installing a just-in-time method and a factory automation system. When the method and system as stated above are installed, it is important to prevent a trouble and a stop of equipment in each process.
As one of causes of trouble occurrence, there can be cited instability of electric power caused by disasters due to daily natural phenomena such as thunderbolt and gust of wind (so-called as an “instantaneous voltage drop (voltage sag)”). As for the instability of the electric power, it has been tried to avoid by duplexing of a power supply path, a backup power supply, and so on.
However, in case of a small-to-medium sized plant, an uninterruptible power supply (UPS) has been installed in order of importance based on analysis of processes in accordance with an averaged operation to save cost and space. Besides, there is a case when turning on/off of the power supply is manually performed based on thunder forecast or the like from the Meteorological Agency.